Varifocal lens mount with deformable anti-friction coatings

ABSTRACT

A varifocal lens including a cam cylinder rotatably mounted on a stationary housing, and lenses held in lens barrels slideably positioned within the stationary housing to vary the focal length of the varifocal lens. Cam followers to position the lens barrels extend from the lens barrels to guide grooves in the stationary housing and cam grooves in the cam cylinders. The sliding surfaces of the lens barrels and the cam followers are provided with a layer of resilient material having a low coefficient of friction. The dimensions of the lens barrel sliding surfaces and the cam followers are made larger than the dimensions of the members which they contact, so that the resilient material will be slightly deformed and thereby take up the play between the lens barrels and cam followers and their respective coacting members.

0R ateeatosa v allow U Iida [54] VARIFOCAL LENS MOUNT WITH DEFORMABLEANTI-FRICTION COATINGS [72] Inventor: Yozo lida, Tokyo, Japan [73]Assignee: Nippon Kogaltu K.K., Tokyo. Japan [22] Filed: July 29, 1970[21] Appl. No.: 59,144

1 May 16, 1972 [57] ABSTRACT A varifocal lens including a cam cylinderrotatably mounted on a stationary housing, and lenses held in lensbarrels slideably positioned within the stationary housing to vary thefocal length of the varifocal lens. Cam followers to position the lensbarrels extend from the lens barrels to guide grooves in the stationaryhousing and cam grooves in the cam cylinders. The sliding surfaces ofthe lens barrels and the cam followers are provided with a layer ofresilient material having a low coefficient of friction. The dimensionsof the lens barrel sliding surfaces and the cam followers are madelarger than the dimensions of the members which they contact, so thatthe resilient material will be slightly deformed and thereby take up theplay between the lens barrels and cam followers and their respectivecoacting members.

6 Claims, 4 Drawing Figures PATENTEDIAY 161912 3, 663 O93 INVEN TOR Yozo110A ATTORNEY VARIFOCAL LENS MOUNT WITH DEFORMABLE ANTI- FRICTIONCOATINGS FIELD OF THE INVENTION This invention relates to a lens mountfor a varifocal lens assembly which assembly varies its focal length byslidably moving the lens mount along the optical axis ofthe assembly.

DESCRIPTION OF THE PRIOR ART The zooming mechanism for a varifocal lensusually consists of a cam cylinder rotatably mounted on a stationarylens housing. Lenses to vary the focal length are held in movable lensbarrels mounted in the stationary lens housing. Pins or cam followersextend from the movable lens barrels through guide grooves in thehousing and into cam grooves in the cam cylinder, so that rotation ofthe cam cylinder will move the lens barrels axially within thestationary housing, thereby changing the focal length of the varifocallens.

In order to reduce the torque necessary to rotate the cam cylinder, thefrictional force between the cam grooves and cam followers in minimizedby using a roller instead of a pin for the cam follower. Also, the slopeof the cam groove is made as small as possible.

However, the slope of the cam groove cannot be made too small withoutrequiring either excessive turning of the cam cylinder or unduly complexmechanism to position the lens barrels within the housing. Further, whena roller cam follower is used, there is play not only between the rollerand the cam groove, but also between the roller and its shaft. As theslope of the cam groove becomes greater, this play increases in thedirection of the optical axis of the varifocal lens. This play along theoptical axis between the cam follower and cam groove may prevent stablemovement of the barrel and produce an error in image position.

SUMMARY OF THE INVENTION The principal object of the present inventionis to eliminate such defects as described above. According to one aspectof the present invention, the sliding parts of the zooming mechanism aremade of a synthetic resilient resin having a low coefficient of frictionp, less than 0.3 Also, the slide members to be fitted into the camgroove and the stationary lens housing have outer diameters which arelarger than the width of the cam groove and the inner diameter of thestationary lens housing respectively. Therefore, there exists no playbetween the cam follower and the cam groove and between the movablebarrel and the stationary lens housing, so that the movable barrels maybe moved smoothly with a higher degree of accuracy.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal sectional viewof a zoom lens assembly embodying the present invention;

FIG. 2 is a sectional view looking in the direction indicated by thearrows II in FIG. 1;

FIG. 3 is a schematic representation of the relationship between theconventional guide groove, cam groove and cam follower; and

FIG. 4 is a schematic representation of the relationship between theguide groove, cam groove and cam follower in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, anobjective lens 2 is mounted upon a camera 1. A front or focus lens mount5a mounting a front or focus lens 5 is in threaded engagement at 4 witha stationary lens housing 3 of the objective lens 2 so that the focuslens 5 may be axially moved. Within the housing 3 are disposed lensgroups 6 and 7 in such a manner that they may be moved toward or awayfrom each other so as to continuously vary the focal length and tothereby vary the degree of magnification of the varifocal lens. Astationary lens group 8 is mounted coaxially ofthe above-mentionedlenses 5, 6 and 7 in the housing 3.

Movable lens groups 6 and 7 are mounted upon movable "lens barrels 9 and10, respectively, which slide in the stationary housing 3. A resilientsynthetic resin having a small coeffcient of friction (i.e. less than0.3 such a tetraflouroethylene resin, is used to form slide members 11and 12 which are fixed to the outer peripheral surfaces of the movablebarrels 9 and 10 respectively. (See FIG. 2). It should be noted that themaximum diameter of the movable barrels 9 and 10 including the slidemembers 11 and I2 is a few microns to 0.1mm larger than the innerdiameter of the lens housing 3. The movable barrels 9 and 10 aredeformably fitted into the lens housing 3 by utilizing the elasticdeformation of the slide members 11 and 12 so that there is no gap orplay when the movable barrels 9 ad 10 move in the lens housing 3.

Slide members 13' and 14' are formed on cam followers 13 and 14 wichextend from the movable barrels 9 and 10 respectively. These slidemembers are made of the same synthethic resin as the slide members 11and 12 and have an outer diameter about a few microns to 0.3mm largerthan the width of guide grooves 15 and 16 formed in the axial directionin the lens housing 3 and the cam grooves 18 and 19 formed in a camcylinder 17. It is therefore readily seen that these cam followers 13and 14 may be fitted into the guide grooves 15 and 16 and cam grooves 18and 19 without any play.

The cam cylinder 17 is rotatable but not axially movable over the lenshousing 3 and has the cam grooves on its periphery. Since the shape ofthe cam groove 18 is different from that of the cam groove 19, relativeaxial movement between the movable lens groups 6 and 7 is produced byrotation of the cam cylinder 17, thereby obtaining a continuouslyvariable magnification. A varifocal ring 20 is securely fixed to the camcylinder 17. Focusing is provided by rotating the focusing ring 21.

Since the slide members 13' and 14' are yieldingly fitted into the camgrooves 18 and 19 and into the guide grooves 15 and 16, the tolerancerequired in machining these grooves may be sufficiently compensated forby the deformation of the synthetic resin.

FIG. 3 illustrates the relationship between the guide grooves 15, 16,the cam grooves 18, 19 and the cam follower 22 of a conventionalvarifocal lens in a relatively high zoom ratio position. Because the camfollower and the cam grooves are fonned of relatively non-deformablematerial, the manufacturing tolerances of these members which arenecessitated for their proper coaction result in play X and X betweenthe cam follower 22 and respectively the cam grooves 18, 19 and theguide grooves 15, 16. The play X in the direction of the optical axis 23will increase with an increase in the cam groove angle 0- formed betweenthe line 25 perpendicular to the optical axis and the line 24 parallelto the direction of the cam groove 18,19. If the anglea were to increaseto so that the play X would become X, then the play in the direction ofthe optical axis would become infinite.

As shown in FIG. 4, the cam follower 13 or 14 used in the presentinvention has a slide member 13' or 14' respectively which forms thecontacting surface of the cam follower. The slide members 13' and 14'are formed of the same type of resilient synthetic resin having a lowcoefficient of friction as the slide members 11 and 12. The slidemembers 13' and 14' of the cam followers are larger than the grooves 15and 18 or 16 and 19 in which they travel and are deformed at points Aand B in order to fit into and move in the grooves. Therefore, therewill be no play at all between the slide members and the grooves duringthe zooming operation.

According to the present invention, play, waving, flutter, etc. of thesliding pans may prevented during zooming operation so that the constantand stable image position may be maintained. The slide members arefitted into the grooves by utilizing the elastic defonnation thereof sothat the parts are not required to be machined and surface-finished witha higher degree of accuracy. Therefore, the fabrication of the parts ismuch facilitated.

What is claimed is:

l. A lens system providing a continuously variable focal lengthcomprising a stationary lens housing having a guide groove; a cam tubehaving a cam groove therein, rotatably supported about the stationarylens housing; a movable lens barrel means within and slideably supportedby the stationary lens housing and including first slide member meansforming the contact surface of the movable lens barrel means with thestationary lens housing; follower means extending from the movable lensbarrel means to coact with the guide groove and the cam groove to movethe movable lens barrel means along the guide groove upon rotation ofthe cam tube, the follower means including second slide member meansforming the contacting surface of the follower means with the guidegroove and cam groove; the first and the second slide member means beingformed of a resilient material having a low coefficient of friction; themovable lens barrel means sized with relation to the stationary lenshousing to require slight deformation of the first slide member meanswhen slideably supported within the housing; and the follower meanssized with relation to at least one of the guide groove and cam grooveto require slight deformation of the second slide member means whencoacting with the guide groove and cam groove, so that the resiliency ofthe first and second slide member means will take up play between themovable lens barrel means, the follower means and their respectivecoacting surfaces.

2. The lens systems providing a continuously variable focal lengthaccording to claim 5 wherein the first and second slide All i I" i emember means are formed from a material having a coefficient of frictionof less than 0.3.

3. The lens system providing a continuously variable focal lengthaccording to claim 6 wherein the first and second slide member means areformed of tetrafluoroethylene resin.

4. The lens system providing a continuously variable focal lengthaccording to claim 5 further comprising a first and'a second movablelens barrel means within and slideably supported by the stationary lenshousing; and each movable lens barrel means including first slide membermeans forming the contacting the surface with the stationary lenshousing.

5. The lens system providing a continuously variable focal lengthaccording to claim 8 wherein the stationary lens housing includes afirst and a second guide groove; the cam tube includes a first and asecond cam groove; the first movable lens barrel means includes a firstfollower means coactin g with the first guide and cam grooves; thesecond movable lens barrel means includes a second follower meanscoacting with the second guide and cam grooves; and each of the followermeans includes a second slide member means forming the contactingsurface for each of the follower means with the coacting guide and camgrooves.

6. The lens system providing a continuously variable focal lengthaccording to claim 5 wherein the first slide member means is deformednot more than 0.1mm and the second slide member means is deformed notmore than 0.3mm.

t t: t s a:

1. A lens system providing a continuously variable focal lengthcomprising a stationary lens housing having a guide groove; a cam tubehaving a cam groove therein, rotatably supported about the stationarylens housing; a movable lens barrel means within and slideably supportedby the stationary lens housing and including first slide member meansforming the contact surface of the movable lens barrel means with thestationary lens housing; follower means extending from the movable lensbarrel means to coact with the guide groove and the cam groove to movethe movable lens barrel means along the guide groove upon rotation ofthe cam tube, the follower means including second slide member meansforming the contacting surface of the follower means with the guidegroove and cam groove; the first and the second slide member means beingformed of a resilient material having a low coefficient of friction; themovable lens barrel means sized with relation to the stationary lenshousing to require slight deformation of the first slide member meanswhen slideably supported within the housing; and the follower meanssized with relation to at least one of the guide groove and cam grooveto require slight deformation of the second slide member means whencoacting with the guide groove and cam groove, so that the resiliency ofthe first and second slide member means will take up play between themovable lens barrel means, the follower means and their respectivecoacting surfaces.
 2. The lens systems providing a continuously variablefocal length according to claim 5 wherein the first and second slidemember means are formed from a material having a coefficient of frictionof less than 0.3.
 3. The lens system providing a continuously variablefocal length according to claim 6 wherein the first and second slidemember means are formed of tetrafluoroethylene resin.
 4. The lens systemproviding a continuously variable focal length according to claim 5further comprising a first and a second movable lens barrel means withinand slideably supported by the stationary lens housing; and each movablelens barrel means including first slide member means forming thecontacting the surface with the stationary lens housing.
 5. The lenssystem providing a continuously variable focal length according to claim8 wherein the stationary lens housing includes a first and a secondguide groove; the cam tube includes a first and a second cam groove; thefirst movable lens barrel means includes a first follower means coactingwith the first guide and cam grooves; the second movable lens barrelmeans includes a second follower means coacting with the second guideand cam grooves; and each of the follower meanS includes a second slidemember means forming the contacting surface for each of the followermeans with the coacting guide and cam grooves.
 6. The lens systemproviding a continuously variable focal length according to claim 5wherein the first slide member means is deformed not more than 0.1mm andthe second slide member means is deformed not more than 0.3mm.